Abstract: A packing element for a biological filter or for use in mass transfer has a plurality of trickling faces along which the liquid or gas to be treated flows. The faces are disposed on at least one rim of the element at an angle between 3.degree. and 40.degree. relative to the vertical axis of the element, and have relatively large surface areas. The apex angle of the element is about 140.degree. to about 180.degree., the height of the element being greatest at its center portion. Rounded projecting portions cause randomly introduced elements to become oriented automatically so that the vertical axis is aligned with the liquid or gas flow and the element in a horizontal position. Additionally, a ductlike member is provided at the upper edge on at least one of the at least one rims, to more effectively distribute the liquid or gas flow on the trickling faces.